Error detector for telegraph printers



Feb 11, .J. A. SPENCER ERROR DETECTOR FOR TELEGRAPH PRINTERS Filed March50, 1958 2 Sheets-Sheet l INVENTOR. JAMES/1. SPENCER ATTORNEY.

Rab. J. A. SPENCER 9 31397 ERROR DETECTOR FOR TELEGRAPH PRINTERS FiledMarch 50. 193B 2 Sheets-Sheet 2 mg I -n mu 3 Z 4;

INVENTOR. 73 67 JAMES A. SPENCER ATTORNEY.

Patented Feb. 11, 1941 UNITED STATES I canon nr'rao'ron roa TELEGRAPHPRINTERS James A. Spencer, Teaneck, N. 1., assignor to Radio Corporationof America, a corporation of Delaware Application March 30, 1938, SerialNo. 198,809

. 14 Claims.

This invention relates to error detectors and has particularly to dowith means associated with a printing telegraph receiving apparatus fordetecting errors of transmission of code signals, also for detecting theoccurrence of fading conditions when telegraph code signals aretransmitted over a radio channel.

This application is a continuation in part of my co-pending application,Serial No. 147,398, filed June 10, 1937, which issued April 11, 1939 asPatent No. 2,153,737.

It is an object of my invention to provide means for detectinginstancesof mutilation of code signals and to provide means for controlling ateletypewriter in such manner as to prevent the printing of charactersin response to mutilated signals. It is a further object of my inventionto provide a system for causing an error designating character to beprinted in place of an intelligence bearing character in response toeither the reception of a mutilated signal or otherwise in response to afading condition on a radio channel.

While the principles involved in carrying out my invention are largelycommon to the parent application and to this continuation case, I haveherein shown a specific embodiment of the invention which has been foundparticularly useful due to its adaptability to printing telegraphreceivers of a conventional type. v

As in the parent application, so also in this case, I prefer to make useof a signalling code having equal intervals for each character andhaving preferably seven or eight time intervals allotted to each codesignal so that a fixed number of marking time intervals may always bepresent in each code signal.

A code signalling system in which the signals are of equal length andpossess a fixed ratio other than 1 to 1 between the number of markingand spacing units thereof has been disclosed in U. S. Patent No.2,183,147, granted Dec. 12, 1939 to John B. Moore and Richard E. Mathes.

A telegraph printer adapted to be actuated by code signals of uniformlength and having as many as seven or eight time elements in each codesignal would require, of course, an equal number of selector bars. Asexplained in the application of Moore, et al. above referred to, it isdesirable that a fixed number of selector bars be actuated in making theselection of any charactor to be printed. If a shift key, is employed,then seven units in the code signal would be suflicient. If no shift keyis employed, then eight units would be required for differentlycharacterizing each code signal for ordinary communications purposes. Myinvention has particularly to do with a novel means for counting thenumber of marking impulses in each code signal so that if the fixednumber of such impulses is three, them the reception of any code signalhaving more or 5 less than three marking impulses would be efiectiveupon the error detecting device of my invention so as to enable thereceiving printer to print an error indicating character in place of theintended character. 10

I have found that an electrical circuit arrangement for carrying out theobjects of my invention. is preferable to a purely mechanical structurewhich might be designed for obtaining similar results. If the markingimpulses are mechanil5 cally counted, it is true that it is possible todetect the errors which may occur in transmission, but an objection tothe use of mechanical means lies in the problems of maintenance of sucha system as well as problems of maintaining a suitable 20 printingspeed. My invention is free from these objections because it operates onthe bwis of current differentials resulting from the completion of adefinite number of circuits, each completion being upon reception of a.marking impulse. The 25 error detector, therefore, operates under thecontrol of the received signal.

My invention will now be described in more detail, reference being madeto the accompanying drawings in which Figure 1 shows a. fragmentary planview of a series of contact springs associated with the selector bars ofa conventional printing telegraph instrument;

Fig. 2 shows a front elevation of the contact 3 springs, the selectorbars, and associated apparatus for use in error detection; and

Fig. 3 shows schematically an end view elevation of the contact springs,the code selector bars, a pull bar and lever mechanism connecting with a40 type bar of the printer, which type bar may be used for errordetection and may be restrained from making a stroke by means of anelectromagnet in response to the reception of a correct code signal. 45

In the description to follow, like parts are given, like referencenumerals in the several figures. Although the invention is hereinillustrated by only one embodiment, the several figures are presentedfor more clearly showing the structural 50 details fromdifferent pointsof view.

Telegraph typewriters adapted to print characters in response tofive-unit code signals have been in general use for sometime. When,however, it was discovered that a seven-, or eightunit code had certainadvantaga for purposes of error detection, it became necessary toincrease the number of code selector bars from five to'at,

mounted in ways 3 so that they may be actuated by a slight longitudinalmovement in response to the code signals. The various cuts or notches 5in the code bars are so arranged that when the code bars are adjusted inresponse to a code signal all seven of the notches 5 are opposed to oneparticular pull bar, or type selector I for selecting the same and foractuating a type bar 9.

Now, according to my invention, thereis provided a series of contactsprings and I3 disposed in pairs, each pair being associated with one ofthe code bars I respectively. The contact springs are preferably mountedin a holder I5 of insulating material and may be clamped together in theusual manner for a spring pile-up." Considering each pair of contactsprings the spring II is relatively stiff, while the spring I3 isrelatively flexible and is provided with a rearwardly extending portioncarrying an insulator II. A certain spring tension causes the spring I3and its insulator ll to be urged against a shoulder I9 on the code barto be disclosed in this continuation application.- Furthermore, I havefound that certain modifications of the error detecting circuitarrangement are desirable and they will, therefore, now be described.

Connected with each of the contact springs I3 is a resistor 2|. Theseveral resistors 2| are of like value and all are fed with energy fromany suitable current source, the positive terminal of which is hereshown connected to a common conductor 23. The companion contacts II areconnected in parallel to a common conductor 25 leading to a relay 21which is serially connected through the windings of two further relays29 and 3|. The ground connection beyond the relay 3| may be consideredthe same as the negative terminal of the source.

The relays 21, 29 and 3| are biased by springs 33 whose tensions aresuitably adjusted for causing each of the relays to respond to currentsof different amplitude. The adjustments of these spring tensions are,therefore, made suitable for causing relay 21 to operate on a currentstrength equal to the current passed through one or more of theresistors 2|. Relay 29 is adjusted to operate on a current strengthequal to the total current passed through exactly three of the resistors2|. Relay 3| is adjusted to operate only on a current strength equal tothe total current passed by at least to of the resistors 2|.

It will be remembered that in carrying out my invention I preferablyutilize seven-unit code signals in which every signal is characterizedby the presence of exactly three marking impulses. The relays 21, 29 and3| are provided with circuit arrangements through their associatedcontact springs for operating a magnet 35 whose armature 75 31 ispivoted at 39. A lever member 4| which supports the armature 31 normallyholds the armature away from the core-piece of the magnet 35 undertension of a spring 43. A push rod 45 is connected at one end to thelever arm 4| and is supported at the other end by a bracket 43 havingslot 49 opposite the pull bar 1e so that no matter what combination ofmarking and spacing elements may be set up on the code bars there isalways an open space at 49 for the pull bar I. to drop into, provided itis not restrained from so doing by the actuation of the magnet 35 andthe forward movement of the push rod 45. It will, therefore, be seenthat for normal reception of intelligence-bearing telegraph signals themagnet 35 should be energized each time a character is to be printed.When, however, a code signal becomes mutilated, or even if it drops outdue ,to fading, it is required that the magnet 35 shall not be energizedand that the error designating type bar 90 shall be actuated. Thecircuit for controlling the magnet 35 will now be described.

The positive terminal of a direct current source leads through aresistor 5| to the winding of the magnet 35 and thence to the movablecontacts of relays 21 and 3|. The back contact of relay 21 is groundedas is the negative side of the operating source. The front contact ofrelay 29 isalso grounded. The back contact of relay 3| is connected tothe movable contact of relay 29. If desired, a capacitor 53 may beconnected in shunt with the winding of the magnet 35 for reducingcontact sparking at the relays.

When unmutilated signals are received, namely, signals uniformly bearingthree marking impulses, the current flowing through the conductor 25which is derived from the source through three of the resistors 2| inparallel is just sufficient to actuate relays 21 and 29 but isinsulllcient to actuate relay 3|. Under this condition an energizingcurrent for magnet 35 will flow through the tongue and back contact ofrelay 3|, the tongue and front contact of relay 29 and thence to ground.If, however, the signal is mutilated so that only one or two markingimpulses are received, then fewer than three pairs of contacts ||I3 willbe closed and the current flow through less than three of the resistors2| will be insuflicient to actuate either of the relays 29, 3|.

The dropping out of one or two marking impulses in a seven-unit codesignal. therefore, results in a de-energization of the magnet 35, sinceits actuating circuit is broken by the release of relay 29 and also bythe pulling up of the armature of relay 21. Hence, there is no groundconnection for a return circuit from the magnet 35. Under this conditionthe push rod 45 assumes a withdrawn position with respect to the pullbar 12. The pull bar I; is, therefore, permitted to drop into thenotches 49 of the seven code bars and actuation of the error symbol typebar is effected. This type bar may also be actuated by de-energizationof the magnet 35 when a static impulse is superimposed upon thetransmitted signal, thereby increasing the number of marking impulses inthe code signal to four or more. Under these conditions the excesscurrent supplied through four or more of the resistors 2| and throughcontacts which are closed between the springs II and I3 for differentcode bars will sponse to a marking impulse have been moved into positionfor opening up an alignment of notches 5 opposite one of the pull barsI, this selected pull bar is permitted to drop into the code bar notchesunder the tension of a spring 51. Immediately the printing ball 59 israised and its associated printing bail roller 6| is also pushed up intothe notches 63 inback of each pull bar I. As the selected pull bar dropsinto the notches of the code bar I the printing ball 59 engages with ashoulder 65 on the pull bar. Hence the pull bar I is lifted and swingsthe type bar actuator 61 upwardly about the pivot center 69. Thetype bar9 swings on the pivot center 'II and is caused to make a. stroke againstthe paper by the upward movement of the pin 13 which is supported at theend of the actuating bar 61. All of the pull bars 1 are substantiallyalike and function in the same manner. There is just one fundamentaldifference, however, between the selection of the error designating typebar 9e and the selection of any other type bar. The difference residesin the manner inwhich the error designating pull bar 1e is controlledcompared with the normal control of the other pull bars by directselection of the code bars I. In the case of the error pull bar 1e thereis always an open alignment of notches 49 in the code bars I. But whenproper intelligence-bearing signals are received the magnet 35restrainsthe pull bar 1e from entering the'notches 49. When an error occurs, thewithdrawal of the push rod 45 enables the pull bar I; to enter thenotches 49, thus providing a selection of the error designating type barfor printing an error designating symbol.

Under certain conditions as in testing the operability of the telegraphcircuits and radio channels, it is useful to employ the relay 21 forshowing the occurrence -of mutilated signals of the kind where one ortwo of the marking impulses are dropped out. Itis apparent that whenonly the relay '2! is actuated and relays 29 and 3| are not actuated,then no closed circuit through the magnet 35 is obtainable. Thiscondition occurs when the received code signal consists of one or twomarking impulses only. In order to differentiate, therefore, betweensignal mutilations of this type and a complete absence of signals theswitch 55 must be closed so that the magnet 35 will be energized if nosignals are received. Of course, under this condition there would be nooperation of the error designating type bar.

It is quite'generally desired, however, that in the operation of a radiocommunications circuit a monitoring idle-time signal shall beperiodically repeated so that in case such a monitoring signal shouldnot be received, notice will be given at the receiving station ofabnormalities or fading conditionsin the telegraph circuit or in theradio channel. In order to provide for differentiating between a properspacing signal as transmitted from the point of origin of acommunication and complete fading of the signal at the receiver, it isrequired that the circuit through the tongue of relay 21 be opened as byopening the switch 95. Under these conditions although the errordetecting circuit through the resistors 2| includes. the seriallyconnected windings of the relays 21, 29 and 2|, nevertheless only therelays 29 and ii are effective to control the magnet because the switchI5 is opened.

It will be seen that the reception of an unmutilated-code signalconstituted by threemark ing impulses and four spacing impulses resultsin the actuation of relay 29 while relay 9| remains unactuated. Magnet35 is energized as before stated. However, if neither or both of therelays 29 and 3| are actuated then the circuit through magnet 35 isopened and the printing of an error designating symbol results.

The idle-time signal which was hereinbefore mentioned should, of course,be one which contains three marking impulses, but which is a specificsignal not otherwise used for the transmission of intelligence. So longas either intelligence signals or idle-time signals are received, theerrordesignating type bar is re.- strained from operation. If, however,either a mutilated signal is received or if no signal is received, thenthe synchronous actuation of the printer will be such as to cause theerror-designating symbol to be typed.

The principles and method of operation of my invention are notrestricted to the use of any particular telegraph typewriter structure.It is well known that a number of different embodiments of telegraphprinters are operable by'mcans of type selectors under control ofdifierent forms of code element responsive devices. Some of thesetelegraph typewriter-embodiments operate on the start-stop principlewhile others are adapted to operate in response to the reception ofsynchronous multiplex signals. My invention is, therefore, adaptable toany of these difierent embodiments of telegraph typewriters includingthose which possess type bars as well as those which operate with typewheels.

Several jpractical advantages result from the improvements herein shownas compared with the original embodiment of my invention which wasdescribed and shown in the parent application aforementioned. Amongthese advantages it may be mentioned that by employing contacts H and I3which are directly controllable by the code bars of the printingtelegraph instrument not only are electrical failures detected by theoperation of the error type bar, but mechanical failures of the printingtelegraph apparatus itself may also be detected.

Another advantage resides in the provision for distinguishing betweenspace signals and fading. When a space signal is transmitted as betweenwords and sentences, three of the code bars I are selected forobstructing all of the pull bars 1 from entering any of the notches 5,with the exception of the error designating pull bar 1e. This pull bar1e, however, is normally obstructed by the actuation of the magnet 35.But when fading occurs, the magnet 35 is lie-energized, and the pull bar1e becomes operative, provided the switch 55 is left open.

Still another advantage of the improvements herein shown and describedover the arrangement of the parent application is that of simplicity ofconstruction. In the improved embodiment it is no longer required thatthe contacts ll-l3 shall be controlled by independent relays in responseto the reception of the various marking impulses of each code signal.

Varlous modifications of my invention may suggest themselves to thoseskilled in the art upon a review of the disclosure as herein given..However, the scope ofpthe invention itself is to be understood ashaving all the breadth that is permitted by the claims. 1

I claim:

1. An error detecting device for a telegraph printer comprising aplurality of contact elements arranged in pairs, each pair beingcloseable by the operation of an appropriate code-bar in saidp'rinter,.means responsive to'the movement of a prescribed number ofsaid code-bars into selecting positions for printing a character, andmeans operable by the closure or a number of said contact pairs otherthan said prescribed number within a time interval allotted to thedecoding of a single multi-element code signal for indicating amutilation of said signal.

2. An error detecting device for a telegraph printer comprising aplurality of parallel-circuited resistors, a relaylsystem operable inseries with a selected number of said resistors, means directly operableby the code bars of said printer for energizing said relay systemthrough selected ones of said resistors, and means variably controlledby said relay system ior.indicating a departure from a prescribed numberof code bar operations within a time interval allotted to the de-codingof a single multi-element code signal.

3. A device for detecting telegraph signal mutilations comprising atelegraph printer responsive to un-mutilated equal-length code signals,an error-designating type-bar in said printer, a plurality of code barspermutationally selectable upon reception of marking impulses in eachcode signal, a variably resistive circuit arrangement including contactsmechanically closeable by said code bars, and means operable throughsaid circuit for causing the error-designating type bar to be actuatedwhenever the number or received marking impulses differs from the numberprescribed for an un-mutilated code signal.

4. A device according to claim 3 and having further means operablethrough said circuit for causing the error-designating type-bar to beactuated upon the occurrence of a code-signal transmission with respectto which all the marking impulses have faded out.

5. In combination with a telegraph typewriter having code-selector bars,pull-bars and type bars mutually cooperative in response touniformlength code signals for transcribing intelligence,

an error-designating type bar, an error pull-bar for said error typebar, said error pull-bar being mechanically independent of said codebars, a magnet having means controlled by its armature for blocking theerror pull-bar, and means responsive to the reception of an un-mutilatedcode signal for actuating said magnet thereby to prevent the operationof said error pull-bar and error-designating type bar.

6. In combination with a telegraph typewriter having code-selector bars,pull-bars and type bars mutually cooperative in response touniformlength code signals for transcribing intelligence, anerror-designating type bar, an error pull-bar for said error type bar,said error pull-bar being mechanically independent of said code bars, amagnet having means controlled by its armature for blocking the errorpull bar, and means operative in the event'oi fading of any or all ofthe transmitted marking impulses appropriate to one of said code signalsfor disabling said magnet thereby to unblock the error pull-bar and thusto enable the error-designating type-bar to operate.

7. Incomblnation with a telegraph typewriter having code-selector bars,pull-bars and type bars mutually cooperative in response touniformlength code signals for transcribing intelligence, anerror-designating type bar, an error pull-bar for said error type bar.said error pull-bar being mechanically independent or said code bars, amagnet having means controlled by its armature for blocking the errorpull-bar, and means operative upon receipt of a signal which ismutilated by the introduction therein oi spurious marking impulses forrendering said magnet inactive, thereby to unblock the error pull-barand thus to enable the error-designating type-bar to operate.

8. In a printing telegraph receiving system, a

. printer having de-coding'members movable from non-selecting toselecting positions in response to the reception of marking elements ofa signal, and character-printing devices selectively actuable inaccordance with the permutational ad- Justment of said de-coding membersto selecting positions, a plurality of pairs of contacts each pair beingcloseable by the movement of an appropriate one .0! said de-codingmembers to a selecting position, a resistor in circuit wth each contactpair respectively, an error-detecting relay system operable by closureof any of said contact pairs, the manner of operation of said systembeing dependent upon the number of said resistors which are connected inparallel by said contact closure, a magnet under control oi saiderrordetecting relay system, means for printing an error-symbol, andmechanism cooperating with said magnet in response to the reception of asingle un-mutilated signal, when characterized as such by said relaysystem, for preventing the operation of said error-symbol printingmeans.

9. A device in accordance with claim 8 and having means operable inresponse to the reception 01 a mutilated signal also in the event offading of a transmitted code signal for enabling the error-symbolprinting means to operate.

10. In a printing telegraph receiving system, a printer having characterselecting means responsive to a hired normal number of marking elementsof a uniform-length code signal, means for detecting instances ofmutilation and instances of fading of the code signals, said meanscomprising a relay operable by said character selecting means uponreceipt of at least the normal number of marking impulses in a singleone of said code signals, a second relay operable by said characterselecting means only upon receipt of a superfluous marking impulse insaid code signal, and means responsive to the simultaneous operation ofboth said relays and responsive also upon failure of both said relays tooperate at the expected time of reception of a code signal for causingan error-designating character to be printed.

11. In the operation of a telegraph printer having a plurality of codeselector members each movable to a selecting position in response to thereception of a marking element of an equal length code signal, themethod of indicating a discrepancy between the transmission andreception over a communications channel of an unrepeated one of saidsignals, which comprises utilizing the movements of said code selectormembers to condition a sensing device for controlling the amplitude ofan electric current, and causing an excess or deficiency in saidamplitude with respect to a normal value to produce an indication ofsaid discrepancy.

12. In the operation 01' a telegraph printer having a code selectormember for each element of an equal length signal to be de-coded, andhaving type members including an error-designating type member, themethod of actuating said errordesgnating type member in response to thereception of an unrepeated one of said signals and in lieu of anintended actuation of one of the other type selectors, which comprisespermitting one of said code signals to be mutilated by the addition of aspurious impulse or by nullifying the receiving response to atransmitted marking element, causing said code selector members tocooperate in controlling the amplitude of an electric current, andcausing said error-designating type selector to be actuated in responseto a departure of said current from a normal value.

13. A telegraph printer having code selector bars and type bars, incombination with a plurality of circuit closing devices eachindividually controlled by the actuation of an appropriate code selectorbar, means variably operable in accordance with the number of circuitclosures by said devices for differentiating between the reception ofun-mutilated and mutilated code signals, and an error indicating deviceoperable by said difierentiating means upon reception of a mutilatedsignal for conditioning a particular one of said type bars to beactuated.

14, A telegraph printer comprising a plurality of code selectorbars,.means for setting said selector bars in positions corresponding tothe marking and spacing elements of a received code signal, a pluralityof type bars any one of which is selectable by an appropriatepermutational setting of said code selector bars, an error designatingtype bar, and means conditioned by said code selector bars uponreception of a mutilated signal for causing the error designating typebar to be actuated, the last said means including a plurality of circuitclosing devices each device being operable under control of anappropriate code selector bar, and including marginal relays variablyoperable in accordance with the number of said devices which areoperated.

JAMES A. SPENCER.

